1. Field of the Invention
The present invention relates to a lubricating system for a gear train provided in a gear unit, such as a gear box, a high-speed gear mechanism or the like, used in a gas-turbine engine or jet engine.
2. Background Art
The gear unit of this type has a lubricating oil supply port provided for spraying lubricating oil toward each gear in order to lubricate and cool the gear, and a lubricating oil discharge port provided for recovering the lubricating oil remaining after a lubricating and cooling operation, with an oil-discharge pump. As the loss of power generated in this gear unit, one caused by air resistance associated with rotation of each gear and another caused by resistance associated with stirring the lubricating oil are mainly known. Especially, in the case of an aircraft engine, the gear train is rotated at a relatively high speed, generating considerably increased air resistance. Additionally, with recent conspicuous acceleration of introducing various electric and electronic equipment or units into the body of each aircraft, it can be expected that dramatic increase of the capacity of power generation will be required in the near future. Of course, in such a case, the loss of power due to the air resistance generated by the rotation of each gear and/or resistance associated with stirring the lubricating oil will also be increased. This may significantly increase negative impact on the fuel consumption of the aircraft engine, such as the jet engine, gas-turbine engine or the like.
To reduce the aforementioned loss of power in the gear unit, a gear shroud system, in which a plurality of gears, respectively meshed with one another in the gear train, are covered with a shroud, has been proposed (see Patent Document 1: JP4-503558A). This shroud system is intended to reduce the air resistance by controlling or positively suppressing generation of a reverse-tornado-shaped spiral air flow that would be otherwise likely to be drawn along a front face of each rotated gear and then generated on a front face side of the gear. Specifically, the shroud of this system includes a pair of side walls, each opposed to a side face of each gear, while extending adjacent an outer diametrical face of the gear, and an end wall arranged to be vertical to the pair of side walls, while extending parallel to the front face of each gear. In other words, these side walls and end wall are respectively arranged to surround each front face of the plurality of gears in the gear train. In addition, a first opening for injecting the lubricating oil toward each gear and a second opening for discharging the lubricating oil from the shroud are provided in the end wall, respectively. Namely, with this shroud system provided adjacent to the teeth of each gear, the generation of the aforementioned spiral air flow on the front face side of each gear can be positively controlled. Therefore, the air resistance can be significantly reduced.
In order to effectively reduce the air resistance and resistance associated with stirring the lubricating oil, it is necessary that the above shroud covering the respective gears in the gear train has a shape suitable for smoothly introducing the lubricating oil into the discharge port without causing undue residence of the lubricating oil and then efficiently discharging the lubricating oil from the discharge port. If the discharge port is provided in an unsuitable position of the shroud, the residence of an excessive amount of the lubricating oil would occur in the shroud, leading to substantial increase of the loss of power, irrespectively of the provision of the shroud. It is true that the shroud disclosed in the Patent Document 1 can positively control the generation of the aforementioned spiral air flow. However, this technique is essentially aimed at enhancing the cooling effect of the lubricating oil by using the shroud. Namely, in this Patent Document 1, there is no study and/or suggestion for smoothly introducing the lubricating oil into the discharge port and efficiently discharging the oil from the discharge port.